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Author Topic: Webcam - Video Encoding Load?  (Read 2453 times)
debio
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« on: July 02, 2009, 01:36:50 PM »

I'm considering using my Sheevaplug (ordered, not delivered) to host a USB webcam for remote access, but I'm wondering if it's powerful enough to do live video encoding. More specifically, I wonder if the lack of a hardware FPU will cripple it.
I don't recall if it's possible to get raw image data from a camera (I think it was with some, but not with others?), but I would think that the best approach would probably be to encode raw video to XVid on the fly. The lower quality approach would be to stream JPEGs (I know that's only supported by some cameras, but mine supports it).
Anyway, how would something like this go?
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mcginnist
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« Reply #1 on: July 02, 2009, 02:32:58 PM »

I've used mjpg-streamer to pipe 4 640x480 usb webcam streams at 30fps to zoneminder (running on another machine) without issue.

Attempted to re-encode just one stream to something a windows media player would play and that brought the plug to it's knees.
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davall
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« Reply #2 on: July 03, 2009, 02:40:07 AM »

I'm using motion on a debian driven plug without any problems.
Give it a try. Great peace of software.

Greets, davall
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ReverseEngineered
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« Reply #3 on: July 21, 2009, 08:17:47 AM »

I haven't tried this yet (my plug should be delivered today), but I don't see why it wouldn't encode most formats.  A definite exception could be MPEG4, since it's known for taking a lot of CPU resources to encode.  Try sticking to something simpler like MPEG2 or MJPEG and it should work.  I've read reports that this chip is about the same power as a P3 and there were lots of people running PVR systems on P3s.
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debio
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« Reply #4 on: July 21, 2009, 11:43:18 AM »

The problem isn't CPU power, the problem is that there is no hardware FPU (Floating Point Unit) to process floating point values quickly. As a consequence, the CPU must do floating point calculations, which is much much slower. Lossy encoding, such as video encoding, generally uses floating point values.
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Rabeeh Khoury
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« Reply #5 on: July 22, 2009, 04:40:33 AM »

debio - video encoding typically uses integer or SIMD instructions for doing some heavy matrix conversion like DCT or I-DCT.

Right?

If so then the floating point is not needed.

For Audio there are MP3 encoders that uses floating point (like lame) and there are others that uses integer based codec.
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debio
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« Reply #6 on: July 22, 2009, 05:04:59 AM »

I'm not sure where floating point operations are and aren't used, but I do know that lossy codecs tend to use them, and basically any significant floating point use will kill the plug. It's floating point performance is probably below that of the original Pentium (although it doesn't have a division glitch like the Pentium had).
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